The present invention relates to miniaturized dielectric resonators for VHF to microwave regions (30 MHz to 10 GHz, referred to hereunder as a high frequency region) and, more particularly, to a resonator of this kind featured by low loss even when the dielectric constant of the resonator is high.
High dielectric constant ceramics with low loss and high stability have recently been in use to miniaturize high frequency apparatus and to improve its reliability. Particularly, the trend toward the extensive use of integrated circuits has accelerated the development of highly miniaturized narrow-band, low-loss bandpass filters, which can be composed of strip lines formed on a ceramic substrate of a high dielectric constant. (For details, reference is made to T. D. Iveland, "Dielectric Resonator Filters for Application in Microwave Integrated Circuits," published in IEEE Trans. on Microwave Theory and Techniques Vol. MTT-19, No. 7, pages 643 to 652, July 1971). The conventional dielectric resonators for the high frequency region are generally classified as a coaxial dielectric resonator and a circular cylindrical or rectangular parallelepiped dielectric resonator. (Reference is made to J. C. Sethares et al, "Design of Microwave Dielectric Resonators", IEEE Trans. on Microwave Theory and Techniques, Vol. MTT-14, No. 1, pages 2 to 7, January 1966). The circular cylindrical or rectangular parallelepiped dielectric resonator is particularly suited for miniaturized resonators of high unloaded Q for the frequency range from several GHz to 10 GHz. In contrast, this type of resonator is difficult to miniaturize in the 300 MHz to 3 GHz region if a comparable unloaded Q is desired to be maintained. The coaxial dielectric resonator for the UHF region is easier to miniaturize but it is difficult to maintain high unloaded Q values.